Michael Howard's attempt to refocus the election campaign on the issues of asylum and immigration was undermined today by one of his former ministerial colleagues, Charles Wardle, who described the Tory leader's policies as unworkable and uncosted.

The former Tory immigration minister told reporters at a Labour party press conference that Mr Howard's policies are "uncosted, unworkable and likely to make immigration and asylum problems worse not better".

Mr Wardle's comments came as the latest Observer/MORI opinion poll put Labour seven points ahead of the Conservatives, on a comfortable 40%, with the Tories on 33% and the Liberal Democrats on 19%.

With immigration one of the few issues the Tories lead Labour on, Mr Howard has repeatedly sought to make it the centre of his campaigning, accusing Tony Blair today of "pussyfooting" around the problem.

The Tory leader told GMTV's Sunday programme: "Immigration today is out of control and that is a matter of great concern for the future of good community relations in Britain."

Hew added: "We think it is something a government needs to get hold on that's why we would set an annual limit on the number of people who could come in to the country."

The Tory leader raised the issue again this afternoon when he warned Tory supporters in Telford that there are "literally millions of people in poorer countries" who will try and settle in Britain without a limit of the number allowed into the country.

Mr Howard's proposal that parliament set an annual cap on the number of migrants allowed into the country each year, which would involve pulling out of the UN convention on refugees, was dismissed however by his former Home Office colleague.

Mr Wardle, who had invited himself to a Labour party press conference, said that "it almost defies belief that Mr Howard is standing before people and presenting this as a policy proposal".

"It is the most half baked, incoherent package imaginable. It shows he is utterly unsuited for the for the position of prime minister."

While dismissing the Tory proposals, Mr Wardle praised Labour's plans to deal with immigration and asylum, calling them "substantial, thought-through and likely to be effective".

Labour's election co-ordinator, Alan Milburn, later echoed Mr Wardle's comments, when he told the BBC Politics show: "If you have got a proposal which says you are going to cut the immigration and asylum budget in half, which is what they are planning, how on earth is that going to protect Britain's borders."

The Liberal Democrat leader, Charles Kennedy, also questioned Mr Howard's motives for repeatedly raising the issue of asylum, telling BBC Breakfast with Frost that politicians should "talk about people's hopes in this election, lets not talk people's fears".

Mr Kennedy was speaking ahead of a rally of his party's candidates in London, where he promised that the Liberal Democrats would concentrate on positive campaigning and avoid "yah-boo politics".

Mr Blair, meanwhile, accepted his local party's nomination in Sedgefield today, telling activists that education was still the key to Britain's future economic prosperity and the government's priority.